A substantial volume of blood is shed during many major surgical procedures, such as heart by-pass surgery and hip replacement surgery. Often the shed blood, which has been contaminated, is discarded and replaced with donor blood. An alternative procedure has been developed in which the shed blood is recovered, the contaminants removed, and the "uncontaminated" blood cells reinfused into the patient.
In this procedure, the fluid in the surgical site is collected using suction and is drawn into an evacuated reservoir. The fluid collected in the reservoir, called "shed blood", contains whole blood, saline used to rinse the surgical site, blood clots, bone chips, fatty tissue, anti-coagulants and other miscellaneous contaminants.
The collected shed blood may be disposed of in at least three ways. First, it may be discarded and the lost blood volume replaced by donor blood.
A second alternative is to filter the shed blood and transfuse it to the patient. The filter removes blood clots, bone chips and tissue from the shed blood, but the filtered shed blood remains diluted with the saline originally used to rinse the surgical site.
The third alternative is to "wash" the shed blood, as well as filter it. One way of washing shed blood is to use a centrifugal wash system. (See "The Preparation of Leukocyte-Poor Red Blood Cells: A Comparative Study", Meryman et al., Transfusion 20(3):285:287 (1980).) In a typical centrifugal wash system, shed blood is centrifugated while washing it with saline in a disposable centrifuge bowl or rotor. A typical bowl for such a system is the so-called Lathan bowl, shown in U.S. Pat. No. 4,300,717. Since red cells have a higher density than saline, platelets, white cells or blood plasma, the red cells fill the outermost portion of the rotating centrifuge bowl. As more shed blood enters the bowl, the red cells remain in the bowl displacing the supernatant (saline, plasma, platelets, anti-coagulants, etc.) out of the bowl. Next, saline is directed into the bowl, instead of shed blood. Saline, entering the bowl, is directed by the lower extended skirt portion of the core of the bowl to the outermost radius of the bowl and through the bed of packed red blood cells. In this way, the supernatant is diluted and displaced by the saline until a satisfactory "washout" efficiency is obtained.
The various fluids are directed into and out of the bowl by peristaltic pump(s). The pump(s) comprise a motor driven rotor with rollers disposed opposite a stationary platen. Flexible fluid pathways formed by plastic tubing are occluded between the platen and the rollers. As the pump rotor rotates, the rollers cause the tubing to alternately contract and expand to propel the fluid in the tubing along a desired path. Various sections of the flexible tubing are also opened or closed by hydraulic or pneumatic valves to control the fluid flow.